Rehabilitation doses delivered in concentrated daily bursts have shown some promise in infants and children with Cerebral Palsy (CP) but a systematic examination of this dosing efficacy has not been carried out. At least 3 factors require rigorous scientific examination: (a) the frequency-response relationships where improvement is measured not only in terms of motor function but also in other domains such as cognition; (b) whether therapy effects can be maintained over time; and (c) the patient characteristics associated with differential response to dose. The proposed project is informed by a theoretical path model of dosing and a preliminary study on concentrated daily therapy and weekly therapy for the purposes of establishing the infrastructure to support this research. We will randomize 75 infants with CP, 6 - 24 months of age and GMFCS III-V (higher severity), to determine the short-term and long-term effects of 3 dosing protocols consisting of an identical number of 2-hour sessions of the same motor learning-based therapy applied over a different total number of calendar weeks: (a) 2 hours of therapy one day per week for 20 weeks (usual weekly group), (b) 2 hours of therapy 3 days per week for 6.6 weeks (intermediate group) and (c) 2 hours of therapy every weekday for 4 weeks (concentrated daily group). The specific aims are: 1) to compare short-term (6 months following initiation of therapy) and long-term (1, 1.5, and 2 years following the initiation of therapy) outcomes in terms of gross motor function, domains of development, goal attainment scaling, and spontaneous play; and 2) to identify factors that predict individual differences in outcomes for children with CP with the two dosing protocols. Of particular interest are individual child characteristics including age, severity leve, and parent preferences. Innovative aspects of the proposed project are the conceptual framework, the study design, and the use of comprehensive outcome measures including spontaneous play, a skill inherent to child development, and goal attainment scaling, for evaluating activity- and participation-level skills. The proposed project tests a theoretical principle that frequency of rehabilitation is an important regulator of therapeutic response in infants and does not test the efficacy of a type of treatment. The results will inform clinicians, families, and scientists about dosing and will provide much-needed recommendations for frequency of rehabilitation in order to optimize motor function and development of young children with CP.